This invention relates to an apparatus and method for the deposition of thin-film materials used in the fabrication of thin film integrated circuit devices, and thin film devices made according to the method and with the apparatus.
In the fabrication of thin film (TF) IC devices, such as thin film transistors (TFTs), a method and apparatus is needed to form the various layers constituting the device. Silicon material, typically amorphous silicon (a-Si) or polysilicon, are used for the active layers of the device and silicon-based insulating layers, typically silicon nitride, SiNx, or silicon oxide, SiOx, are typically used as insulators between the active layers. There are several methods to deposit these films. Some methods rely on chemical reactions between one or more suitable gas-phase species to deposit the silicon-based film on the substrate where TF devices are to be fabricated. These reactions require energy, which may be supplied in the form of thermal energy, such as chemical vapor deposition (CVD), plasma energy, such as plasma-enhanced CVD (PE-CVD). photon energy, such as photo-enhanced, or laser-pyrolysis CVD, or the presence of a catalyst, as in the case of hot-wire CVD.
Another category of deposition methods are the so-called physical vapor deposition (PVD) methods. In one case, the desired material is deposited by bombarding a suitable xe2x80x9ctargetxe2x80x9d of this material with atoms of sufficient energy, of a typically neutral or inert gas element. This process is called sputtering and is typically accomplished by forming gas plasma in a gap between a target material and the substrate where the material is to be deposited. Argon is the most common gas used in the sputtering industry. Sputtering is a well-suited method for the formation of the various silicon-based, TF device layers because: (1) it is a safe and environmentally benign technique; (2) it may be used at room temperature and is therefore compatible with any type of substrate; (3) silicon films with very low H2 content may be typically deposited and there is no need for dehydrogenation to release excessive hydrogen, or, hydrogen may be incorporated into the film if, and when, necessary; (4) it is a simpler and more easily scaled method than competitive methods, which rely on chemistry; and (5) it has been successfully used for metal depositions in TF devices, such as TFT-LCDs.
There are, however, some problems associated with silicon sputtering. When Ar, at concentrations of  greater than 1 at % (atomic percent), is used as the sputtering gas, capture of Ar by the sputtered film causes structural defects, which lessens the quality of the deposited film. This phenomena reduces the performance of an amorphous silicon (a-Si) TFT device, and also causes difficulties in the crystallization of a-Si, a necessary step in polysilicon TFT technology.
Intrinsic silicon is a resistive material, which, when combined with sputtering in DC mode, leads to the requirement of a significant voltage drop to maintain a given DC power set point. This problem complicates the design of a power supply, increasing the probability of arcing and increasing the extent of plasma damage on the deposited film due to bombardment by highly energized neutral or charged species.
If He is used as the sputtering gas, to eliminate Ar capture and related issues, the deposition rate of the Si or silicon alloy film is significantly reduced, making it unsuitable for mass. production.
Silicon deposition by sputtering has not yet reached manufacturing level. As a result, there is no globally accepted solution to these issues. The main concerns are achievement of a reasonable deposition rate, i.e.,  greater than 10 xc3x85/s (angstroms/sec), low Ar content and good plasma characteristics to reduce plasma damage to the deposited films.
U.S. Pat. No. 5,248,630 to Serikawa et al., granted Sep. 28, 1993, for
Thin film silicon semiconductor device and process for producing thereof, describes construction of a thin film device including deposition of a thin film polycrystalline film.
U.S. Pat. No. 5,665,210 to Yamazaki, granted Sep. 9, 1997, for Method of forming insulating films, capacitances and semiconductor devices, describes deposition of metal oxides and nitride films by RF magnetron sputtering with an atmosphere of less than or equal to 25 at % of inert gas.
U.S. Pat. No. 5,817,550 to Carey et al., granted Oct. 6, 1998, for Method for formation of Thin Film Transistors on plastic substrates, describes TFT construction on polymer materials.
T. Serikawa, Enhanced step coverage of SiO2 films sputtered in hydrogen-argon mixed gas, compares thin films deposited in a 30% H-70% Ar atmosphere with those in pure Ar. Japanese Journal of Applied Physics, Vol. 19, No. 5, May 1980, ppL259-L260.
T. Serikawa et al., Properties of magnetron-sputtered silicon nitride films, describes deposition of thin films of 100 nm to 200 nm thickness at 200xc2x0 C. from a silicon target in a N-Ar mixture. J. Electrochem. Soc., December 1984, pp2928-2933.
A. Okamoto et al., Magnetron-sputtered silicon films for gate electrodes in MOS devices, describes properties of deposited materials under various Ar concentrations. J. Electrochem. Soc., June 1987, pp1479-1484. See FIG. 3.
S. Suyama et al., Electrical characteristics of MOSFETs utilizing oxygen-argon sputter-deposited gate oxide films, describes deposition techniques at low temperature (200xc2x0 C.) to form triode MOSFETs. IEEE Transactions on Electronic Devices, Vol. ED-34, No. 10, October 1987, pp2124-2128.
T. Serikawa et al., Low-temperature fabrication of high-mobility poly-Si TFTs for large-area LCDs, describes formation of TFTs using laser irradiation. IEEE Transactions on Electronic Devices, Vol. 36, No. 9, September 1989, pp1929-1933.
C. S. McCormick et aL, Low temperature fabrication of amorphous silicon thin film transistors by DC reactive magnetron sputtering, J. Vac. Sci Technol. September/October 1997, pp2770-2775.
D. P. Gosain et al., Poly-Si TFTfabrication and hydrogenation using a process compatible with plastic substrates, describes TFT formation on polymer substrates. Electrochem Soc. Proc. vol. 98-22, 1998, pp174-185.
G. K. Giust et al., Low-temperature polysilicon thin-film transistors fabricated from laser-processed sputtered-silicon films, describes an aluminum top-gate coplanar TFT using excimer lasers. IEEE Electronic Device Letters, Vol. 19, No. 9, September 1998, pp343-344.
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A method of physical vapor deposition includes selecting a target material; mixing at least two gases to form a sputtering gas mixture, wherein a first sputtering gas is helium and a second sputtering gas is taken from the gases consisting of neon, argon krypton, xenon and radon; forming a plasma in the sputtering gas mixture atmosphere to sputter atoms from the target material to the substrate thereby forming a layer of target material on the substrate; and annealing the substrate and the deposited layer thereon.
An improved physical vapor deposition vacuum chamber includes a target held in a target holder, a substrate held in a substrate holder, a plasma arc generator, and heating rods. A sputtering gas feed system is provided for introducing a mixture of sputtering gases into the chamber; as is a vacuum mechanism comprising at least one turbomolecular pump for evacuating the chamber to a pressure of less than 16 mTorr during deposition. The method and apparatus are particularly suited for forming thin film transistors and liquid crystal displays having thin film transistors therein.
An object of the invention is to provide an apparatus and method of forming thin film devices in an Ar-containing atmosphere while controlling capture of Ar atoms in the thin film.
Another object of the invention is to achieve a reasonable deposition rate, i.e.,  greater than 10 xc3x85/s (angstroms/sec).
A further object of the invention is to produce a thin film device having a low Ar content.